Abstract: Pollen morohology of 20 species and three varieties in Polygonum seet. Aconogonon Meisn. (Polygonaceae) in China was examined under light microscope (LM) and scanning electron microscope (SEM). The pollen grains are 3-colpate, 3-colporate, polyplicate, or pantocolpate in shape, 20.4 ~ 44.0 µm x 17.0 ~ 34.0 µm, mostly spheroidal to subprolate, rarely oblate-spheroidal or prolate (P/E = 1.06 ~ 1.40). The ornamentation of exine is microspinulose-foveolate, prominently spinulose, coarsely reticulate, or rugulate under SEM. Based on their features of the apertures and the exine sculpturing, the pollen grains can be divided into 5 types, i.e. Aconogonontype, Campanulatum-type, Sibiricum-type, Polystachyum-type and Forrestii-type. A key to the pollen types was provided. The Acontogonon-type is characterized by being 3-zonocolpate and having an imperforate tectum with the microspinulose-foveolate ornamentation. Pollen grains of this type occur in 14 species and two varieties, i.e.P. ajanense, P. alpinum, P. angustifolium, P.cathayanum, P. coriarium, P. divaricatum, P. hookeri, P. lichiangense, P. limosum, P.molle, P. molle var. frondosum, P. molle var. rude, P. ocreatum, P. songaricum, P. tibeticum, P. tortuosum. The Campanulatum-type is characterized by being 6-pantocolpate and having an imperforate tectum with the microspinulose-foveolate ornamentation. Pollen grains of this type occur in two taxa, P. campanulatum and P. campanulatum var. fulvidum. The Sibiricum-type is characterized by being 3-zonocolporate and having a rugulate ornamentation. Pollen grains of this type occur in one species, P. sibiricum. The Polystachyum-type is characterized by being 6( ~ 8)-zonocolpate and having a coarsely reticulate exine ornamentation. Pollen grains of this type occur in two species, P. pinetorum and P. polystachyum. The Forrestii-type is characterized by being 12-pantocolpate and having a prominently spinulose exine ornamentation. Pollen grains of this type occur in two species, P. forrestii Diels and P. nummularifolium. The present results show that the pollen morphology in sect. Aconogonon is of important systematic value. The treatment of this section as an independent genus and the generic status of Knorringia are supported; Polygonum nummularifolium and P. forrestii may be better transferred to the genus Koenigia, while P. pinetorum and P. polystachyum retained in the genus Polygonum.

Key words: Pollen morphology, Polygonum sect. Aconogonon, Polygonaceae, China